Project Summary (Abstract) This four-year project combines the assets of a leading academic medical center (Johns Hopkins Medicine) with those of a recognized international leader in diagnostic excellence (Society to Improve Diagnosis in Medicine [SIDM]) and a major physician specialty society (American College of Emergency Physicians [ACEP]) to break new ground in operational measurement of patient harms linked to diagnostic error. To achieve the goal of improved patient outcomes through diagnostic excellence, it is essential to be able to measure diagnostic performance. Diagnostic errors are the largest cause of preventable harms in US medical care, affecting an estimated 12 million people each year, causing permanent disability or death in at least 0.5 million. Diagnostic safety is a priority research area for AHRQ and the National Academy of Medicine (NAM). A key impediment to ?moving the needle? on reducing harms from diagnostic error is the lack of measures that matter to both patients and clinicians, yet can be fully operationalized (i.e., routinely monitored in the existing workflow). Impactful diagnostic outcome measures would assess serious morbidity and mortality in clinical contexts where diagnostic errors are known to occur. Ideal measures would be specific, valid, precise, and comparable across institutions to facilitate benchmarking that identifies both low and high outlier performers. This proposal uses a novel approach to constructing evidence-based diagnostic outcome measures with readily-available administrative and claims data sets. The Symptom-disease Pair Analysis of Diagnostic Error (?SPADE?) method first identifies a clinically-plausible relationship between a common presenting symptom and a dangerous underlying disease (e.g., chest pain-heart attack, fever-sepsis, dizziness-stroke). It then searches for a statistically-valid pattern of unexpected adverse events (e.g., observed greater than expected short-term inpatient hospitalization following a treat-and-release emergency department [ED] visit). Once such patterns are confirmed, they can be monitored to assess the impact of interventions to improve diagnosis. This proposal seeks to mature a partially-developed SPADE measure (for dizziness-stroke, a frequent cause of serious misdiagnosis-related harms) to the point of readiness for use in national benchmarking of hospital-level diagnostic performance for quality improvement. This SPADE pair has been validated through detailed chart review and statistical testing using data from four Johns Hopkins hospitals, and the National Quality Forum (NQF) has named this measure as a top priority for immediate development. This project will advance the measure towards broad adoption with two Specific Aims: (1) engage key national stakeholders to optimize attributes of the missed stroke measure (via expert panel and emergency physician survey) and (2) measure diagnostic performance of US hospital EDs using the refined missed stroke measure (via Medicare data analysis). These Aims will address stroke misdiagnosis now and, also, yield generalizable scientific insights. This will streamline future development of new measures of harm for other important symptom-disease pairs.